Among women whose breast cancer continued to spread (metastasize) after treatment, adding the cancer drug Afinitor to a hormone drug called Aromasin more than doubled the time before the disease got worse.

Among women with untreated metastatic breast cancer, adding the experimental drug pertuzumab to the breast cancer drug Herceptin and chemotherapy increased the time before the cancer progressed.

In both studies, women given the combination treatments lived a matter of months, not years, longer before their cancer got worse.

"But eventually all women with metastatic disease get worse. These are some of the best data we've seen here. The drugs could be game changers," says Jose Baselga, MD, PhD, chief of oncology and hematology at Massachusetts General Hospital in Boston.

Baselga worked on both studies, presented here at the San Antonio Breast Cancer Symposium and published online by The New England Journal of Medicine.

The First Study: Afinitor Plus Aromasin

Afinitor blocks a protein that some cancer cells need to divide, multiply, and spread. It's already used to treat advanced kidney cancer and other tumors.

Aromasin blocks an enzyme the body uses to make estrogen. It's approved by the FDA to reduce the risk of cancer recurrence in certain postmenopausal women.

At the meeting, Baselga reported that cancer got worse in women given Aromasin and Afinitor after an average of about seven-and-a-half months, compared with just over three months for those given Aromasin alone.

The most common serious side effects of Afinitor were mouth ulcers, shortness of breath, and anemia. Still, the side effects are not as severe as those associated with traditional chemo, he tells WebMD.

"This is the first study to ever show a benefit in these women," Edith Perez, MD, of the Mayo Clinic in Jacksonville, Fla., tells WebMD. She was not involved with the work.

The study included 724 postmenopausal women with a certain type of tumor fueled by estrogen.

Each year, about 220,000 women around the world are diagnosed with this type of advanced breast cancer.

The study, known as BOLERO-2, was stopped early because the women taking Afinitor did so much better.

Novartis, which makes the drug and funded the study, is applying for approval for this use. But because both drugs are commercially available, they could be prescribed by doctors already.

Baselga consults for a number of drug companies, including Novartis and Genentech.

The Second Study: One-Two Punch With Pertuzumab, Herceptin

In the second study, adding pertuzumab to a combination of Herceptin and chemotherapy extended the time before cancer got worse from just over a year to just over a year and a half.

Both drugs target a protein called HER2 that is overproduced in certain breast cancers. The drugs work together in a complementary way, Perez says. She has received research funding from Genentech, which makes the drugs and funded the work.

With the exception of diarrhea and a somewhat lower white blood cell count, women on pertuzumab didn't experience more side effects.

Pertuzumab is now being tested as treatment for women with early-stage, HER2-positive breast cancer.

"The challenge going forward will be how best to use the many HER2 therapies now in development," says William Gradishar, MD, director of breast medical oncology at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University in Chicago.

On the basis of this study, a one-two punch with pertuzumab and Herceptin is a logical choice for women with untreated HER2-positive cancer that has spread, he writes in an editorial in The New England Journal of Medicine.

Perez worries that cost will be an issue if insurers won't cover all the new treatments. Herceptin costs about $4,100 a month, Afinitor between $6,500 and $7,000. A price for pertuzumab has not been set, but it is likely to be in that range.